Timing device for synchronizing the slackening of the needle-thread and thread-severing with timing of the tension-slackening for overcast sewing machines

ABSTRACT

A device is disclosed for synchronizing the slackening of the needle-thread tension with the cutting of the thread in a sewing machine, especially a sewing machine of the overcast stitch type. The device comprises a pneumatic assembly controlled by magnetic valves and a characteristic pneumatic delay mechanism is provided in order to provide an exceptionally accurate adjustment of the time during which the discs of the thread-tensioning device are kept open. The whole assembly is constructionally simple and cheap and is fully reliable in service.

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[15] mss iss Conti [451 Jan. 18, i972 [54] TIMING DEVICE FOR [56] mererenm Cited SYNCHRONIZING THE SLACKENING N N OF THE NEEDLE-THREAD AND U STATES FATE TS THREADSEVERING WITH MING 3,528,379 9/1970 Miller et a]. ..1 12/254 THE TENSION-SLA CKENlNG FUR Primary Examinernjames R Bohr OVERCAST SEWING MACHINES mmmey None and None [72] Inventor: Cesare lL. Qonti, Via Varese 18, Milan,

Italy [57] ABSTRACT 22 Fil d; Mm 7 1970 A device is disclosed for synchronizing the slackening of the needle-thread tension with the cutting of the thread in a sew- PP- 29,621 ing machine, especially a sewing machine of the overcast stitch type. The device comprises a pneumatic assembly con- [30] Foreign Application Pflomy Dam trolled by magnetic valves and a characteristic pneumatic delay mechanism is provided in order to provide an excep- API'. 23, Italy tionally accurate adjustment of the time the discs of the thread-tensioning device are kept open. The whole US. "l l is cgnstrucfionally imple and cheap and is re- [51] Int. Cl. ..D05b 65/00 bl i i [5 8] Field of Search 9 Claims, 7 Drawing Figures Pmmmmsmz 3.635180 SHEET 2 OF 4 INVENT R. (ff/4W5 L a/vr/ PATENTED JAN 1 81972 SHEET 3 BF 4 INVENTOR. (Zr/MEL. C'U/Vr/ PATENTEDJAMWZ 635,180

spam 0F 4 IN VENTOR. (279 425 Z. 6 0M? yum we Tram/[ya TIMING DEVICE FOR SYNCIIRONIZING THE SLACKENING OF THE NEEDLE-THREAD AND THREAD- SEVERING WITH TIMING 01F TIIE TENSIGN- SLACKENING FOR OVERCAST SEWING MACHINES The devices as known and used nowadays for obtaining the synchronization between the slackening of the tension of the needle-thread and severing the needleand the shuttle-thread in sewing machines making overcast stitches are either of an electromechanical or a mechanical type.

The timing of the slackening of the tension of the needlethread is usually obtained electrically by relays and electromagnets with a timing capacitor: these are impaired by serious shortcomings in setting due to the exceedingly high tolerances inherent in the capacitors having a high capacitance, such as are necessary, on account of the instability of the capacitive magnitudes and the dielectric fragility thereof.

The temporary slackening of the thread tension is necessary, as is well known, so that the cutter, in its active return stroke, may draw a certain length of thread prior to reaching the cutting position at the counterblade. Said certain length of thread aforesaid is required in order to prevent the thread to be unthreaded from the needle as the sewing operation is resumed.

The mechanical systems have, above all, the limitation that they can be only operated in combination with a threadcutting mechanism of a mechanical control type and their reduction to practice is, of necessity, extremely bulky, intricate and expensive.

Pneumatic control devices are also known, both for the severing cutter and the slackening of the tension of the needlethread, the synchronization and timing step being performed electromagnetically.

According to the invention, a synchronizing device is provided, between the slackening of the tension of the needlethread, with timing of the slackening of the thread tension, for overcast stitch sewing machine, the device being characterized in that it comprises, in combination:

1. A source of compressed air;

2. a magnetic valve fed by said source and controlled by a needle-positioning motor equipped with an appropriate synchronizing contact;

3. a piston for pneumatically controlling the cutter;

4. a piping connecting the magnetic valve with the pneumatic piston which controls the cutter;

5. a pneumatic control piston for the slackening of the tension of the needle-thread;

6. a piping which connects the magnetic valve with the piston which controls the slackening of the tension of the needle-thread;

7. a rate of flow regulator for the discharge of the air of the piston which pneumatically controls the slackening of the tension of the needle-thread;

8. a control line for the magnetic valves, issuing from the switchboard of a needle-positioning motor, said line being controlled, in turn, by an annular synchronizing sector located on one of the machine main shafts.

The basic constructional ideas of the device according to the present invention are:

l. the exploitation of the air discharged by the piston which pneumatically controls the cutter, for actuating the pneumatic control piston for the slackening of the tension of the needle-thread;

2. the circumstance that the rate of flow regulator for the air discharged by the pneumatic control piston for the slackening of the tension of the needle-thread is a pneumatic delay device in proper sense, whose operability is highly reliable and whose constructional embodiment is extremely simple.

The foregoing basic operative features of the invention will be better understood when reading the disclosure of a few preferred embodiments of the invention. These are shown in a diagrammatical fashion and by way of example, without any implied limitation, in the accompanying drawings, wherein:

FIG. 1 is an operative diagram of the pneumatic assembly in the embodiment with a single-acting cutting-control piston, shown both in the idle position and in the position subsequent to thread cutting.

FIG. 2 is a diagram, similar to FIG. 11, and shows the position in readiness for the active return-and-eut stroke.

FIG. 3 is a diagrammatical showing of the pneumatic cutting assembly, with double-acting cutter-controlling piston, in the at rest position and in the subsequent cutting position.

FIG. 4 is a view similar to FIG. 3, but shows the same assembly in readiness for the active return and cutting stroke.

FIG. 5 is the pneumatic flow-diagram of a cutting device in which the cutter-controlling piston is double-acting, according to a modification, in the at rest position and in the position subsequent to thread-cutting.

FIG. 6 is a view similar to FIG. 5, but illustrative of the position of the assembly in readiness for the active return and cutting stroke.

FIG. 7 is an overall diagrammatical. view which shows in a simplified fashion the arrangement of the several members of the pneumatic assembly, in order to show the functional connections in a sewing machine, the latter being also shown diagrammatically only, together with the electric synchronizing device for the needle-positioning motor (this is shown symbolically).

Prior to passing to the detailed description of the several Figures of the drawings, it will be assumed that the operations of the conventional pneumatic cutter-actuating device and of the cutting mechanisms associated therewith are known: as is known, the cutting operation takes place by the agency of the cooperation of a movable blade with a fixed counterblade, the blade being swung in a direction to grasp the thread, then urged against the counterblade to perform the cutting, and eventually brought to the starting position again. In summation, two movements, that is, a forward and a backward movement.

Having now particular reference to FIG. I, the principal component parts of the device can be seen, namely; a source of compressed air, 1, in the form of a. tube section, a threeway, twin-position magnetic valve, 2, the piping 4 connecting the magnetic valve 2 to the piston 3 which controls the cutter (this can be seen, diagrammatically shown at 11, with its counterblade 12, also diagrammatically shown), the piping 6 which connects the magnetic valve 2 to the piston 5 for controlling the slackening of the tension of the needle-thread. Also diagrammatically shown is the stem 8 of the piston with a pointed end adapted to enter the interspace between the discs 9 and 10 of the thread-tensioning device. The diagram of FIG. 1 also shows, in a simplified fashion, at 113, that the piston 3 has a certain degree of freedom: it should be: able to rock about an axis which is perpendicular to the sheet of the drawing in order to follow the movement of the cutter without jamming. Also the electric main T for controlling "the magnetic valve 2 is shown.

The diagram of FIG. I clearly shows how the compressed air enters the magnetic valve 2, reaches the piston 3 and shifts the cutter ill towards the right, as viewed in the drawing. As the magnetic valve 2 cuts off the air feed to the piston 3 which has reached its right-hand end of stroke, after having shifted in that same direction the cutter 11, the latter is biased towards the left by an internally mounted spring and, in the meanwhile, the magnetic valve 2 allows the air discharged by the piston 3 to fill the piston 5 for controlling the slackening of the tension of the needle-thread. As a matter of fact the piston 5, as it is shifted towards the right, causes the pointed end integral with piston stem to be inserted between the discs 9 and 10 of the thread-tensioning mechanism to open the latter and overcoming the bias both of the spring mounted in the interior of piston 5 and the return spring of the tensioning device (not shown). Meanwhile the cutter I1 is brought back to the left and the thread is severed between the cutter blade 11 and the counterblade 12. It has already been said that the position of the cutter as shown in FIG. 1 is both the starting and the end position.

FIG. 2 shows the intermediate position, that is to say, the position at which the cutter 11 has been brought to the extreme right prior to starting the cutting operation.

In order that the operational cycle may be clearly understood, it will suffice that the three stages thereof be recalled, namely:

1. Starting position of FIG. 1; the cutter is at the extreme left.

2. Intermediate position of FIG. 2: the cutter is at the extreme right, and

3. Position of FIG. 1: the cutter is at the extreme left again and return to the starting position once more.

Summarizing now from a strictly pneumatic viewpoint:

l. Feeding air under pressure to the cutter-controlling position 3 only (FIG. 2): the cutter is shifted to the right and is in readiness for grasping the thread.

2. The return spring of piston 3 beings the piston to the left again and discharges it: the air, through the magnetic valve 2, which, meanwhile, has been opened again, to the piston 5 which controls the slackening and opens the discs (FIG. 1): meanwhile, the thread has been severed (FIG. 1) and air begins to be discharged from the piston 5 into the atmosphere through the rate of flow adjusting device 7, whereas the piston 5 is brought to the left once again by its own internally mounted return spring. The device 7 (a restrictor") is a pneumatic delay device proper; it permits, by varying the rate of flow of the air discharged from the piston 5, to adjust the opening time of the discs 9 and 10 of the needle-thread tensioning device according to the necessity of the machine or of quite particular work to be performed.

The device is simple and reliable in operation and its time of action can be adjusted with great accuracy.

It should be observed that, in the intermediate position of FIG. 2, no pneumatic connection is active between the cylinder of the piston 3 and the cylinder of the piston 5.

FIGS. 3 and 4 show the embodiment with a double-acting piston 3 (cutter control): stated in simpler words, the bias of the return spring of piston 3 is replaced by the elasticity of a gas (compressed air). In this flow-diagram, just as in those of FIGS. 1, 2, 5 and 6, the closely spaced dots show high-pressure air, whereas the thinly scattered dots indicate low-pressure air. For the remainder, the operation of the scheme of FIGS. 3 and 4 is very much the same as those of FIGS. 1 and 2: there is, in addition, the main 4a which feeds with high-pressure air the right-hand chamber of piston 3 to shift same piston towards the left (FIG. 3) and, conversely, discharged low-pressure air as the piston 3 is shifted towards the right as a result of the intake of high-pressure air in its left chamber (FIG. 4).

The flow diagram of FIGS. 5 and 6, which is seemingly more intricate, actually reproduces the same operation as those of the embodiments described hereinbefore. There are two magnetic valves, 2 and 2' (of course, in this case, either valve is normally open" and the other is normally closed), placed in parallel with respect to the same electric main T: this electric main serves for physically controlling the magnetic valves in each and every embodiment: otherwise the magnetic valves, if more than one is used, should receive a control pulse from a specially provided pulse generator: this is a part of the conventional art and thus will not be described in detail or shown in the drawings, either.

The arrangement which can be seen in FIGS. 5 and 6 permits a more sophisticated adjustment as is required in certain cases: here also the piston 3 is double-acting. High-pressure air is fed to the piston 3 through the main 4 (FIG. 6), the air is discharged from piston 3 through the line 4b and then into the atmosphere through the magnetic valve 2'. Subsequently, (see FIG. 5) high-pressure air is fed through 2' and 4b to the piston 3 and the latter discharges air, still under a high pressure, through the line 4, the magnetic valve 2 and the line 6, into the piston 5 and actuates the slackening of the tension of the needle-thread. The sequence of the three operational stages of the pneumatic assembly as a whole is also here very much the same as that of the simpler scheme of FIGS. 1 and 2. All of these embodiments show, in a number of forms, the connection between the discharge of the single-acting (or double-act-- ing) cylinder for the cutter-control piston 3 and the loading of the cylinder which controls the slackening of the tension of the needle-thread 5: whenever either cylinder is loaded, the other one is unloaded, when either cylinder is being charged, the other one is being discharged, and vice versa. By so doing, the correct sequence of the operations, viz inactive stroke of the cutter, cutting stroke, and return to the initial position, is assured in any case. The presence of the pneumatic delay device 7 permits, as has been said above, that the duration time of opening of the discs of the tensioning device may be adjusted with extreme accuracy. In FIG. 7, a comprehensive scheme of all the embodiments described hereinabove is reported.

What is claimed is:

l. A thread-cutting and thread-tensioning synchronizing system for a sewing machine apparatus comprising a pneumatically operated thread-cutting device having an air inlet, a pneumatically operated thread tension control device having an air inlet, a source of compressed air, a magnetically operated control valve means connected to said threadcutting device and tension control device and having a first position for connecting said source to the inlet of said thread cutting device and a second position for interconnecting the inlet of said thread-cutting device and the inlet of said thread tension control device, whereby pressure applied to said thread-cutting device in said first position of said valve means is released from said thread-cutting device to operate said thread tension control device in said second position of said valve means.

2. The system of claim 1 further comprising a rate of flow regulator connected to the input of said thread tension control device for releasing pressure at the inlet of the thread tension control device at a determined rate for controlling the period of operation of said thread tension control device.

3. In a sewing machine apparatus of the type having a thread-cutting device, and a thread tension control device, the improvement comprising a first pneumatic control device having an inlet and a pneumatically operated piston operatively connected to control said thread control device, a second pneumatic control device having an inlet and a pneumatically operated piston operatively connected to control said thread tension control device, a source of compressed air, a magnetically operated control valve connected to said source, a first pneumatic connection between said inlet of said first control device and said control valve, a second pneumatic connection between said inlet of said second control device and said control valve, and means biasing the piston of said first control device toward the inlet thereof, said control valve having a first position interconnecting said source and said first pneumatic connection, and a second position interconnecting said first and second pneumatic connections, whereby pressure applied to said first control device in the first position of said control valve is applied from said first control device to operate said second control device in said second position of said control device.

4. The sewing machine apparatus of claim 3 further comprising a rate of flow regulator connected to said second pneumatic connection for releasing air pressure therein at a determined rate for controlling the period of operation of said second control device.

5. The sewing machine apparatus of claim 3 wherein said first pneumatic control device is comprised of a cylinder within which the respective piston is slidably mounted, the respective inlet being located at one end of said cylinder, and wherein said biasing means is comprised of a spring urging said piston towards said one end of said cylinder.

6. The sewing machine apparatus of claim 3 wherein said first pneumatic control device is comprised of a cylinder within which the respective piston is slidably mounted, the respective inlet being positioned in one end of said cylinder, and wherein said biasing means comprises a third pneumatic thread-tensioning discs, characterized in that said second pneumatic control device is comprised of a pneumatic cylinder enclosing the respective pneumatically operated piston, the respective inlet being connected to one end of said cylinder, and wherein the operative connection between the respective piston and said thread tension control device is comprised of a stem on said piston extending through the other end of said cylinder, said stem having a pointed end positioned to enter the interspace between said disks for controlling thread tension.

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1. A thread-cutting and thread-tensioning synchronizing system for a sewing machine apparatus comprising a pneumatically operated thread-cutting device having an air inlet, a pneumatically operated thread tension control device having an air inlet, a source of compressed air, a magnetically operated control valve means connected to said thread-cutting device and tension control device and having a first position for connecting said source to the inlet of said thread cutting device and a second position for interconnecting the inlet of said threadcutting device and the inlet of said thread tension control device, whereby pressure applied to said thread-cutting device in said first position of said valve means is released from said thread-cutting device to operate said thread tension control device in said second position of said valve means.
 2. The system of claim 1 further comprising a rate of flow regulator connected to the input of said thread tension control device for releasing pressure at the inlet of the thread tension control device at a determined rate for controlling the period of operation of said thread tension control device.
 3. In a sewing machine apparatus of the type having a thread-cutting device, and a thread tension control device, the improvement comprising a first pneumatic control device having an inlet and a pneumatically operated piston operatively connected to control said thread control device, a second pneumatic control device having an inlet and a pneumatically operated piston operatively connected to control said thread tension control device, a source of compressed air, a magnetically operated control valve connected to said source, a first pneumatic connection between said inlet of said first control device and Said control valve, a second pneumatic connection between said inlet of said second control device and said control valve, and means biasing the piston of said first control device toward the inlet thereof, said control valve having a first position interconnecting said source and said first pneumatic connection, and a second position interconnecting said first and second pneumatic connections, whereby pressure applied to said first control device in the first position of said control valve is applied from said first control device to operate said second control device in said second position of said control device.
 4. The sewing machine apparatus of claim 3 further comprising a rate of flow regulator connected to said second pneumatic connection for releasing air pressure therein at a determined rate for controlling the period of operation of said second control device.
 5. The sewing machine apparatus of claim 3 wherein said first pneumatic control device is comprised of a cylinder within which the respective piston is slidably mounted, the respective inlet being located at one end of said cylinder, and wherein said biasing means is comprised of a spring urging said piston towards said one end of said cylinder.
 6. The sewing machine apparatus of claim 3 wherein said first pneumatic control device is comprised of a cylinder within which the respective piston is slidably mounted, the respective inlet being positioned in one end of said cylinder, and wherein said biasing means comprises a third pneumatic connection to the other end of said cylinder, and means connecting said third pneumatic connection to said source.
 7. The sewing machine apparatus of claim 6 wherein said third pneumatic connection is connected directly to said source.
 8. The sewing machine apparatus of claim 6 wherein said magnetic control valve comprises means for connecting said third pneumatic connection to said source only in the second position of said valve.
 9. The sewing machine apparatus of claim 3 in which said thread tension control device is of the type having a pair of thread-tensioning discs, characterized in that said second pneumatic control device is comprised of a pneumatic cylinder enclosing the respective pneumatically operated piston, the respective inlet being connected to one end of said cylinder, and wherein the operative connection between the respective piston and said thread tension control device is comprised of a stem on said piston extending through the other end of said cylinder, said stem having a pointed end positioned to enter the interspace between said disks for controlling thread tension. 